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平南碱性玄武岩产于 NE向的区域性断裂中 ,岩石类型有两类 ,一为碧玄岩 ,全岩 K- Ar年龄为 50 .8Ma,含各类包体 ,有以下特征 :1)含地幔岩包体 ,2 ) [Mg]=0 .78,3)在 Fe O/mol- Mgo/mol图解上液相线橄榄石的成分位于 Fo90～ Fo94之间 ,与橄榄岩包体中的橄榄石成分完全一致。4 ) Ni=0 .0 4 ( % ) <0 .0 5( % ) ,5)其熔浆密度为 2 .62 g/cm3,粘度为 2 .52 Pa· s,携带 4 cm直径包体上升的速度为 37.7cm/s,上升的速度较快 ,具原生碧玄岩浆的特点 ,岩浆液相线的温度为12 86℃ ,起源压力为 1.8GPa,玄武岩富集轻稀土可能与地幔性质有关。一为粗面玄武岩 ,不含包体 ,全岩 K- Ar年龄为 4 9.9Ma,岩浆液相线的温度为 1162℃ ,是进化岩浆。玄武岩的 Nd、Sr同位素显示为亏损地幔源区。它们都是大陆拉张环境下的产物 ,与中国东部新生代玄武岩的形成背景一致。
There are two types of rock types in Pingnan basaltic basalts in NE-trending regional faults, one is Bixuan rock, and the K-Ar age is 50.8Ma with all kinds of inclusions. The characteristics are as follows: 1) 2) [Mg] = 0.78, 3) The composition of the liquid-phase olivine lies between Fo90 ~ Fo94 in the diagram of Fe O / mol- Mgo / mol, Olivine composition is exactly the same. 4) Ni = 0. 04 (%) <0. 05 (%), 5) its melt density is 2.62 g / cm3, its viscosity is 2.52 Pa · s, With a velocity of 37.7cm / s. It has the characteristics of primary Bi Xuan magma. The temperature of magmatic liquidus is 1286 ℃ and the source pressure is 1.8GPa. The enrichment of light rare earths by basalt may be related to the properties of mantle. One is a rough basaltic, non-inclusion body. The K-Ar age of the whole rock is 49.9Ma. The temperature of the magmatic liquidus is 1162 ℃, which is the evolution magma. The basalt Nd and Sr isotopes show a depleted mantle source. All of them are the products of the extension of the mainland and coincide with the formation of Cenozoic basalts in eastern China.